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[Sandia Lab News]

Vol. 54, No. 98        May 3, 2002
[Sandia National Laboratories]

Albuquerque, New Mexico 87185-0165    ||   Livermore, California 94550-0969
Tonopah, Nevada; Nevada Test Site; Amarillo, Texas

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Molecular shuttling mimics cellular behavior Tungsten photonic lattice developed Mining locomotive powered with hydrogen Russian, US lab directors meet



Labs researchers observe molecular shuttling that mimics cellular behavior

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By John German

Labs researchers recently created and then examined molecular movements that could evolve into some of the first useful tools at future nanoconstruction sites, where proteins might be shuttled from place to place in tiny chemical wheelbarrows or built upon molecular scaffolding.

Using improved observational methods, the Sandia team watched as huddled receptor -- or grabber -- molecules on a man-made cell membrane rapidly dispersed across the membrane when they latched onto free-floating ligands (chemical particles), then rehuddled when the ligands were removed.

The behavior mimics biological reactions at the cell level, such as immune system response to viral particles, says Darryl Sasaki of Biomolecular Materials & Interfaces Dept. 1140. The work is based on previous research at Sandia to create metal-detecting sensors based on chemical recognition events (www.sandia.gov/media/metal.htm).

The team's observations are published as the cover story in the April 30 issue of the biweekly chemical and biophysics journal Langmuir, and work on a related system recently appeared in Biophysical Journal (November 2001).

For the experiment, the researchers created an artificial cell membrane made of "phospholipid bilayers" -- rows of long molecules that, like empty pop bottles bobbing on water, self-organize into an orderly heads-up/tails-down formation.

They implanted this flat lipid film with specialized lipids carrying tall receptor headgroups -- pincher- or lasso-shaped structures that chemically grab onto free-floating ligands. (See "Receptors team up to signal cellular response" on page 4.)

Then they watched as the receptors reacted to the addition of metal ions, not only for insights into cellular behavior but also for possible nanoscience advances such insights might offer.

At rest in solution the receptor-lipids pooled into aggregate zones between islands of receptor-less lipids.

But when metal ions (lead or copper) were added, the headgroups latched onto the ions, and ZIP!, the receptor-lipids dispersed evenly across the membrane surface as their newly acquired electrostatic charges caused them to become mutually repulsed.

When the metal ions were removed, the wayward receptor-lipids retraced their steps and regrouped into the same aggregated pools.

"When they bind to the metal, they each race away from their nearest neighbor," says Darryl. "When the ions are removed, they race back to where they were."

The process was performed repeatedly on the same membranes with the same result -- reversible reorganization.

Darryl believes the trails the receptor-lipids follow and the pools they return to correspond, quite literally, to the paths of least resistance on the membrane's surface -- areas where the lipid film is more liquid than solid, allowing the traveling lipids to flow like water.

Tracking tiny travelers

Although producing such chemical recognition events on an artificial membrane is not an achievement in itself, examining them with such fidelity is, says Darryl. The Sandia team used novel microscopy and spectroscopic techniques to make the first documented observations of receptor-lipids repeatedly stepping out and then returning home.

Fluorescent pyrene tags were attached to the tails of the receptor-lipids to aid in tracking their travels on the membrane. When the receptors were aggregated -- as seen using fluorescence spectroscopy -- the huddles appeared bright. When the receptors were dispersed, their fluorescent signals were dim.

In addition, the team used an atomic force microscope to map the surface texture, or topography, of the lipid membrane, identifying locations of the tall receptor headgroups that towered 8 angstroms (about one billionth of a meter) higher than the tops of the membrane lipids.

These observations provided unprecedented clarity about the locations of the receptors in both the dispersed and aggregated states, says Darryl.

"We've been able to characterize films as they change their properties at both the macroscale and nanoscale," he says. "It's the first time such a dynamic molecular system has been imaged this way."

As a result of the team's work, he says, scientists will have a better understanding of chemical recognition on cell-like membrane systems.

Perhaps more tantalizing, he says, are the possibilities the new understandings might bring to the nanotechnology community's growing toolbox.

"The idea of using chemical recognition to form specific structures in the membrane may be a potent tool to aid in the development of controllable nanoscale architectures," says Darryl.

If receptor headgroups propelled to and fro by chemical recognition events can be enlisted to hoist molecules and proteins and deposit them in planned locations, he says, designing and building nanosized structures, such as single-molecule-wide wires, might be possible.

And the receptor-lipids' tendencies to follow preferred pathways offer promise for engineered construction of nano-railroad tracks along which a variety of molecular cargo could be recurringly moved, perhaps aboard motor-protein railcars, he says.

If nano-engineers can control these routes, two- or three-dimensional lipid scaffolds might be designed upon which proteins could be laid down to build nanoscale electronic or photonic circuits.

Nano-switching structures might be designed that self-construct and self-destruct based on chemical recognition events.

In addition, researchers have long sought to build cell-like pods that, when injected into a person's blood stream, would recognize diseased cells and release a drug to destroy those cells selectively. Such a capability could revolutionize medical approaches to treating a variety of illnesses.

"By harnessing even a fraction of the capability of cellular membrane recognition systems, it may be possible to build unique sensor systems that are not only rapid and specific in response but also are innately biocompatible," adds Darryl.

Sandia team members include Tina Waggoner, Julie Last (both 1140), and Todd Alam (1811). John German

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Tungsten photonic lattice developed at Sandia changes heat to light

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By Neal Singer

Tungsten-filament bulbs -- the most widely used light source in the world -- are infamous for generating more heat than light.

That is, they radiate more energy in the infrared than in the visible spectrum.

Now a microscopic tungsten lattice -- in effect, a tungsten filament fabricated with an internal crystalline pattern -- developed at Sandia has been shown to have the potential to transmute the majority of this wasted infrared energy (commonly called heat) into the frequencies of visible light.

This would raise the efficiency of an incandescent electric bulb from five percent to greater than 60 percent and greatly reduce the world's most vexing power problem -- excess electrical generating capacity and costs to homeowners caused by inefficient lighting.

The advance -- which shifts emphasis from a photonic lattice's ability to guide light to its capability of stopping other frequencies from passing through it -- also opens the possibility of increased efficiencies in thermal photovoltaic applications (TPV). Using a tungsten lattice as an emitter at desirable frequencies, model calculations showed that the TPV conversion efficiency reached 51 percent compared with 12.6 percent with a blackbody emitter.

The advance, achieved at Sandia by Shawn Lin (1746) and Jim Fleming (1749), is reported in the May 2 Nature.

The imaginative work seems logical in retrospect, though the theory for the effect -- re-partitioning energy between heat and visible light -- remains unexplained. "It's not theoretically predicted," says Jim. "Possible explanations may involve the variation in the speed of light as it propagates through such structures."

The achievement was accomplished by an extension of well-known MEMS (microelectromechanical systems) technologies that themselves have been derived from mature semiconductor technologies. As a result, fabrication of such devices could be cheap and easy.

The most common use postulated for photonic lattices was based on their capability to transmit beams of light at selected frequencies and bend their paths without losing any energy. The structures, most often made out of silicon, consist of tiny bars fabricated to sit astride each other somewhat like Lincoln Logs at pre-set distances and angles that form in effect an artificial crystal. Spacing of the bars allows passage of only certain wavelengths; other wavelengths cannot pass through. Desirable wavelengths not only transmit but also can be changed in direction by creating defects in the artificial crystal that cause the light to follow the defect along like a car passing through a curving tunnel. This meant photonic crystals had potential in optical communications, in which light beams currently carrying telephone messages and data must be converted to electrons -- an expensive process -- to change direction.

That was where published conceptions and economic activity seemed to have stopped.

Meltdown? Apparently not

A further question considered by Shawn and Jim, with assistance from colleagues Ihab El-Kady, Rana Biswas, and Kai-Ming Ho at Ames Laboratories in Iowa, was what happens to other energies that enter the interior of a three-dimensional crystal. If the crystal were built of tungsten -- fabricated by creating a structure of polysilicon, removing some silicon and using chemical vapor deposition to deposit tungsten as a kind of backfill in the mold -- the metal could handle quite high temperatures and have a large and absolute photonic band gap in the visible range where it is already known to emit light. But what would happen to the other, lower-wavelength energies brought in by an electric current? Would the structure melt through the build-up of heat? Or, more desirably, would the thermally excited tungsten atoms reinforce emissions at higher wavelengths, such as in the visible frequency range?

An order-of-magnitude enhancement

Energy at the edge of the photonic band was observed to undergo an order-of-magnitude absorption increase, or enhancement. This meant that energy was being preferentially absorbed into a selected frequency band. Meanwhile periodic metallic-air boundaries led to an extraordinarily large transmission enhancement. Experimental results showed that a large photonic band gap for wavelengths from 8 to 20 microns proved ideally suited for suppressing broadband blackbody radation in the infrared and has the potential to redirect thermal excitation energy into the visible spectrum.

Thus, not only is a more efficient incandescent lamp shown to be possible, but photovoltaics also can be provided with energy from heat-generators that have transposed energy wavelengths into the most optimal frequencies.

All work was performed on commercially available, monitor-grade six-inch silicon wafers. These photonic devices were fabricated in Sandia's Microelectronics Development Laboratory using modifications of the standard CMOS processes originally developed for Sandia's radiation-hardened CMOS (complementary metal-oxide semiconductor) technologies

The work was funded by the Laboratory-Directed Research and Development program through project manager James Gee (6200). Co-principal investigator Jim Moreno (6216) modeled the thermovoltaic results. - - Neal Singer

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Sandia-industry team powers a mining locomotive with pollution-free hydrogen

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By Nancy Garcia

A potentially revolutionary locomotive rolled into the hydrogen-powered age recently on a test track in Reno, Nev., energized by environmentally friendly fuel cells that a Sandia/California team added to the mining vehicle.

"This is the first ever built in the world, and we learned a lot," says Jennifer Chan (8731), lead engineer and project lead since October. "It's a major step." The advance was welcomed by the mining industry, which bestowed a "best of show" award on the locomotive at the Canada Mining Expo last May.

In Reno, the four-ton commercial vehicle, originally designed to operate on battery packs, showed its prowess by pulling a 500-pound section of loose track at a Burlington-Northern (Kappes, Cassiday & Associates) warehouse sidetrack in Reno. The fuel cells supplied 8.5 kW power as the locomotive glided quietly along the 400-foot test track.

Fuel cells combine hydrogen and oxygen to create water, releasing energy but virtually no pollution. Although they are not yet mass-produced, fuel cells are routinely used in such cost-insensitive applications as powering the space shuttle.

In looking for a transportation market "point of entry," the Fuel Cell Institute, which proposed the project, selected mining vehicles as a potential economically viable initial application.

Nearly all mines employ diesel power, requiring expensive ventilation. Replacing diesel with hydrogen-powered vehicles would save an estimated 30-40 percent in ventilation costs, easily offsetting the cost of the fuel cells. "Those costs alone make this very viable economically," says David Barnes, project manager for prime contractor Vehicle Projects.

There might also be benefits to switching electric- and battery-powered mine vehicles for hydrogen-fueled ones, Barnes says. Batteries have to be charged overnight and switched out, while electric vehicles are tethered by long "extension cords" that present a hazard if run over. And if the electricity comes from coal-fired plants, its generation creates pollution.

The two fuel cell stacks, by the Milan-based company Nuvera, each have a maximum output of 7 kW. Sandia designed and built a metal hydride storage system to safely store the volatile hydrogen, absorbed onto a powdered metal alloy known as a "hydride bed" at the relatively low pressure of 150 psi. The bed can hold almost all the contents of six cylinders of hydrogen, which is normally compressed in the canisters to 2,000 psi.

The bed capacity lets the vehicle operate for a full eight-hour shift before requiring refueling above ground (which may take about an hour).

Sandia developed the "balance of plant" as well as the power plant for the locomotive. The balance of plant includes the water-cooling of the fuel cell, heating of the hydride bed (the heat from the fuel cell is used to heat the hydride bed for optimal operation), balance of air and hydrogen supply to the fuel cells, and the controls and safety systems. The power plant includes the integration of the hydride beds and balance of plant with the locomotive.

Following the above-ground safety assessment, the locomotive will be trucked in a temperature-controlled shipping container to Canada, where it will be compared to electric-powered locomotives at Val d'Or, a former metal mine maintained as an underground experimental mine.

"It's a major, major step forward," says mining engineer Harry Bursey of project partner Warren Equipment. "If we handed out knighthoods, one would be involved." He anticipates the project will be a legacy to upcoming mine workers, such as his son, a geologic engineer in tunneling.

"Diesel exhaust fumes are not only uncomfortable," he explains, "they can be bad on health in the confined atmosphere of an underground mine, and in tunneling as well. The application of fuel cells to replacing diesel engines is absolutely vital. It's a very forward-looking solution."

The project's success could pave the way for production of some 150 hydrogen-powered mine vehicles per year.

The next aspect of the project, to begin this summer, is demonstration of a hydrogen-powered 100kW front-loader for mine use.

So far, nine Sandians have worked for two years on the project with the Fuel Cell Propulsion Institute, Vehicle Projects, the University of Nevada, Warren Equipment, Hatch consultants, the Canadian regulatory agency, MSHA, and Placer Dome and KC&A mining companies.

Besides Jennifer, team members include Ray Baldonado (8214), Ken Black (8120), Don Meeker (8724), Dan Morse (8723), Systems Engineering Dept. 8731 Manager Bill Replogle, Ken Stewart (8730), George Thomas (Sandia/California retiree/consultant), Dan Trujillo (8120), and Mark Zimmerman (8731). Jay Keller (8362) coordinates funding through DOE's Office of Power Technology. -- Nancy Garcia

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Lab Directors meeting reflects new relationship

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By Bill Murphy

For Sandians who cut their teeth during the Cold War, it is still, even 10 and more years later, a jarring, extraordinary image: the group photograph of the directors of the Russian and US weapons labs convened for friendly dialogue at Bishop's Lodge north of Santa Fe.

Looking out from the photo are faces of men and women who, not much more than a decade ago, were sworn adversaries, developers and stewards of implements of war the use of which would bring utter destruction to their foes.

This northern New Mexico meeting April 13-16 was actually the second such gathering; the first was held in conjunction with the celebration of Sandia's 50th anniversary in 1999. At that meeting, attendees were limited to lab directors and their staffs; this time, their bosses -- Gen. John Gordon from DOE's National Nuclear Security Administration and Lev Ryabev, First Deputy Minister of Minatom, Russia's atomic energy agency -- were on hand, lending a policy-level viability to the directors' discussions.

Joan Woodard, Sandia's Executive Vice President and Deputy Director, says that many noted a distinct thawing of the atmosphere between the first meetings 10 years ago with the Russian labs and today. In those first meetings, she says, the atmosphere was described, understandably, as having a certain stiffness, a formality of expression, a perceptible sense -- not of distrust -- but of caution. At the meeting last month, she says, the atmosphere was more relaxed; there was more trust, and markedly less subtext of questioning each others' motives for participating.

The fact is, Joan says, the Russian labs and the US labs share many concerns: knowledge preservation, materials control, and nonproliferation are just a few examples. And, of course, the big issue looming over all the directors' discussions: "the new world dynamics," as Joan put it, referring to the post-9/11 geopolitical situation.

At the 1999 meeting, Joan says, the directors talked about a lot of issues, but there was no final report at that time stating that, "We will now do x, y, and z." This time around, she says, with Gordon and Ryabev participating, there was support to take tangible steps to advance lab-to-lab cooperation.

"Having Gen. Gordon and Lev Ryabev there with us made a huge difference," Joan says.

As a result of the policy chiefs' participation, Joan says, two ideas for tangible action emerged from the meeting:

Joan shares an anecdote that, in her mind, sums up the status of US-Russian relationship, both among lab directors and at the nation-to-nation level.

During the discussion, she recalls, Rady Ilkaev, director of VNIIEF (the All-Russian Scientific Research Institute of Experimental Physics), displayed a cartoon with two frames; In the first frame, two dark-suited gentlemen stand rather stiffly apart, not cozy, but not overtly hostile. The caption says, "Not enemies." In the second frame, the two are closer together, smiling, and appear more relaxed in each others' company. The caption: "Partners?" With a question mark.

Ilkaev, Joan says, asked the rhetorical question: "Where are we in this picture? We are 'not enemies.' But are we yet 'partners?'"

"That is the very issue our governments are trying to sort through," Joan says. And meetings such as the Bishop's Lodge gathering, she says, position the national laboratories in both countries to follow their governments' leads as the nature of the relationship evolves. between US, Russia -- Bill Murphy

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Last modified: May 10, 2002


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